Unit 1: Exploring the Nature of Light Phenomena
VII. Developing Additional Central Ideas Based on Evidence
When you look in a mirror, swim in a pool, or enjoy playing with a prism, you are experiencing a variety of light phenomena. In this section, you will develop additional central ideas about reflection, refraction, and dispersion. Then you will use these central ideas to explain an intriguing phenomenon: seeing rainbows in the sky.
A. Exploring reflection phenomena
The word reflection has many meanings in many different contexts. In physics, the word reflection has a specific meaning. Reflection refers to one aspect of what happens when light shines on smooth or rough surfaces.
Question 1.18 What happens when light shines upon a smooth surface?
Equipment: To explore reflection phenomena, obtain a flashlight, flat mirror, table, two straight sticks such as meter sticks, yard sticks, rulers or pencils, a dark room and at least three people with whom to collaborate. Clean the surface of the mirror so that the light reflects from the mirror rather than from dust on the surface.[In a remote learning situation, a student working alone with a clear mirror and two rulers, can place the mirror on a table next to a wall, lean one end of a ruler against the wall, place the other end of that ruler on or next to the mirror, place one end of the other ruler next to the first ruler on or next to the mirror, and hold the flashlight so that it is shining on the mirror at the same angle as the ruler. Move that ruler (and flashlight) at different angles to see how the reflection of the light moves up and down on the wall. Note the angle of the ruler when the reflection on the wall is on the top of the first ruler.]
- Record the Topic of this exploration on your physics notebook page.
- What happens when a flashlight shines on a flat mirror in a dark room?
Note your initial ideas in the Before section of the physics notebook page documenting your exploration of reflection phenomena.
- What can you find out about reflection phenomena by playing with the flashlight and mirror? Keep track of your explorations in the During section of your notebook page.
- Next explore reflection in a particular way: place the flat mirror on the table. Ask group members to each stand on one side of the table as shown in Fig. 1.26
Person 1 is the person holding the flashlight.
Person 2 is the person standing at the other end of the table.
Person 3 is standing at one side of the table. (If there is a fourth person, Person 4 is standing at the other side of the table.)
- Persons 1 and 2 start the activity while Persons 3 and 4 report what happens. After a while switch positions so that everyone experiences what happens in each location.
- How can Person 1 aim the flashlight at the mirror so that light shines on Person 2’s face at the other end of the table?
- When Person 2’s face is lit, who can see light from the flashlight shining on the mirror?
Person 1 with the flashlight?
Person 2